DESCRIPTION: Heterogeneity among children with ADTHD raises concerns about whether it is a unitary disorder that can be differentiated from other psychiatric/cognitive disorders or from behavioral difficulties that represent one end of a normal distribution, but are not a true categorical disorder. Furthermore, little is know regarding the long-term impact of stimulant treatment. To help establish the validity and boundaries of AD/HD, and to examine the impact of stimulant treatment on long-term outcome, this prospective follow-up study focuses on identifying more homogeneous subgroups of patients that might be associated with distinct outcomes. This study will re-evaluate a large sample of clinically-referred children who were diagnosed with AD/HID between 1990 to 1997 using structured diagnostic interviews. Psychiatric comorbidity as well as cognitive and academic functioning were assessed at baseline. The primary goals are a) to conduct a comprehensive clinical re-evaluation of these children to determine their psychiatric, behavioral, and neuropsychological status as adolescents between the ages of 16 to 19 years-old; b) to ascertain the duration and nature of the treatment interventions they received; and c) to identify subgroups of children that are associated with distinct outcomes. As compared to carefully matched community controls, three competing hypotheses will be tested: Clinical outcome in children with AD/HD is accounted for primarily by comorbidity, rather than by the presence and/or severity of AD/HD; 2) Adverse outcome is related to the severity of AD/HD) symptomatology that persists into adolescence; 3) AD/HD during childhood poses increased risk for poor outcome above and beyond that accounted for by comorbidity and/or the persistence of AD/HID symptoms into adolescence. In addition, the extent to which stimulant medication treatment is associated with adolescent substance use/abuse will be examined, and, as compared to controls, the neuropsychological status of subgroups of adolescents who were diagnosed as having AD/HD during childhood will be characterized.